Many of us have been there before: In a boat, with a more experienced angler. A fish is landed. The veteran fisherman glances at the wiggling fish, tosses it back in the lake, and shows just how smart he is.

“That fish right there? Three years old,” he says without missing a beat. “Nice fish for a 3-year-old.”

Magic? Not necessarily.

That angler just knows “the code.” And you can, too.

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For more than 40 years, state fisheries biologists and hatchery staffers have been making it easy to determine the age of many of the state’s stocked landlocked salmon, brook trout and lake trout.

They clip off a predetermined fin or two — different fin clips correspond to different years — and those fins never grow back.

Each year, hundreds of thousands of those “marked” fish are released into Maine lakes, ponds, rivers and streams, joining millions of already stocked (and clipped) fish from previous years.

“I think this process started back in the 1950s in Maine,” explained Gordon “Nels” Kramer, regional fisheries biologist for the Maine Department of Inland Fisheries and Wildlife. “The process came about, I guess, because we wanted a definitive way to determine the age of a particular fish that we stock.”

There are other methods available: Biologists can take a scale from a dead fish and determine a fish’s age. They can also analyze a fish’s otolith — a bony structure behind its brain — and get the same result.

Both methods are time consuming and expensive.

Looking at a fish that has had a fin clipped off, then comparing what year that fin was clipped is nearly instant. And Kramer said the cost of clipping fins off those fish is somewhere between a penny or two cents per fish.

“[We realized] if we came up with a certain year rotation — a four-year rotation in the case of brook trout and salmon — we could instantaneously, in the field, tell how old that fish was, when it was stocked, when it was marked,” said Kramer, who works out of the DIF&W’s Enfield headquarters.

Kramer explained that a salmon or brook trout that is marked in 2010 is missing the same fin as a fish marked in 2006. Since it’s easy to tell the difference between a 6-year-old fish and a 2-year-old fish, for instance, that four-year rotation works fine.

For longer-living, slower-growing lake trout, that rotation has been increased to 11 years. And recently, an angler caught a lake trout that proved to be 31 years old.

Kramer has been clipping the fins off fish for his entire career in the department — more than 30 years.

But for much of that time, he and his co-workers received some much-need help from the community.

“Basically, we would convene a group of 10 ladies … and get ‘em set up,” Kramer said. “We would provide them with the fish and the equipment. And we would direct them as to what fin would be clipped and they would set about doing it, and by the end of the week, we’d generally have 150,000 fish marked.

Fish are anesthetized first, then quickly clipped and sluiced back into fresh water, where they recover rapidly.

That local group of fin-clippers was disbanded after the 2011 effort. While Enfield hatchery personnel stocks more fish now than it did before, many of those landlocked salmon are produced at other hatcheries that have undergone renovations that have made them more efficient.

Cheryl Hatch of Sebeoeis Plantation was among those members of the clipping crew. She said when she was asked to take part in the 1970s, she didn’t think twice about accepting the offer.

“I thought that’d be pretty exciting,” Hatch said recently. “I like that kind of stuff. There was a bunch of women and they were having a good time, so I thought that’d be great.”

Not that the process was always perfect. During the spring clipping, often held in early April, conditions could sometimes be challenging.

“In the spring there’s ice, for God’s sake,” said another longtime member of the crew, Nellie Dwelley of Enfield. “We almost froze. I can remember dipping my pinkie in the coffee to thaw it out.”

Hatch said that in the last years of the operation, her crew was provided with rubber gloves. But even that only helped for a bit: The water they continually reached was typically between 33 and 38 degrees.

“Even when we got gloves, in the spring people would wear mittens or wool gloves under them,” Hatch said.

Hatch said the camaraderie of the women was one reason she looked forward to those annual clipping sessions.

“We sang and people brought in great things to eat,” she said. “Some of the men brought us donuts, and there was coffee. And we always had a big picnic at the end, which was our goal in life [while we were clipping].”

The fin-clipping tools work similarly to nail clippers, and both women said their main requirement was that the DIF&W provide them with tools that were sharp.